It is known in the art to oxidize phenol to p-benzoquinone with oxygen in the presence of a copper ion catalyst and such a process is disclosed in U.S. Pat. No. 3,987,068. In that patent the oxidation is carried out in a nitrile solvent using a complex formed from the copper catalyst and the solvent, and the operating conditions are said to be a temperature of from about 0.degree. to 100.degree. C. and a partial pressure of oxygen of from about 7 to 200 (preferably 14 to 100) atmospheres. As pointed out in U.S. Pat. No. 3,987,068, yield of quinone product increase with increased partial pressure of oxygen and it appears from the data therein that partial pressures of oxygen above about 100 atmospheres are required in order to achieve conversions of phenol to p-benzoquinone on the order of about 75%. Such oxygen pressures are too high to be useful in an economical commercial process because they require special equipment of high capital cost.
U.S. Pat. No. 3,870,731 relates to the oxidation of phenols to benzoquinones in the presence of copper salts as catalysts where an anionic liquid of the catalyst such as thiocyanate, cyanate, cyanide and halogen ions improve catalyst activity. In such reactions a solvent such as water is disclosed and other polar solvents soluble or miscible with water may be used. Such solvents are exemplified by certain amides, alcohols, and sulfoxides. It is also stated that any of the various solvents may be used alone or in combination with water in any desired ratio.
In our U.S. patent application Ser. No. 284,893 filed July 20, 1981 now abandoned and its continuation application Ser. No. 423,984 filed Sept. 27, 1982 now abandoned, we disclose that the copper catalyzed oxidation of a phenol to a p-benzoquinone can be significantly improved by carrying out the reaction in a nitrile solvent and using a divalent copper catalyst promoted with a alkali metal base wherein the molar ratio of base to copper catalyst is no greater than 2.0. Use of about 10% by volume or less of water in the reaction system gives further improvement to the reaction in that selectivity is increased.
In our U.S. patent application Ser. No. 339,965 filed Jan. 18, 1982 we disclose that a copper catalyzed process for oxidation of a phenol to a p-benzoquinone can be significantly improved so as to enable operation at lower, commercially useful pressures and while also achieving an improved selectivity to product, by conducting the oxidation of phenol in the presence of a monovalent copper ion catalyst (e.g. Cu.sup.+) in a conventional solvent system, preferably a nitrile solvent, which is modified with water.